The present invention relates generally to a tray for positioning and holding x-ray film cassettes in a machine for taking x-ray photographs. It is important in the use of x-ray equipment that the film cassette be properly positioned with respect to the collimated x-ray beam so that the x-radiation will impinge upon a selected area of the film and will not fall outside the margins of the film. This is of particular importance when the equipment or system is being utilized in connection with exposure of a portion of a human body because evidence suggests that radiation is harmful to living beings. Thus, it is desirable to avoid unnecessary exposure of parts of the body and improper film positioning which may require repeated exposure. These considerations are expected to become more important as state and federal governments take an increasing interest in the amount of radiation to which a human individual should be exposed.
Generally, a film bearing tray is disposed beneath a table on which the patient is lying. An x-ray generator is located above the patient at a predetermined focal distance from the film. When the x-ray collimator is suitably adjusted, the cross-sectional size and shape of the cone of radiation produced by the generator is no larger at the film level than the size of the film. Thus, if the film is properly positioned, the patient is exposed to radiation only in the area requiring diagnosis or treatment, and is not exposed in adjacent or unnecessary areas.
X-ray systems of this type generally employ a film tray, sometimes called a "Bucky" tray (See BUCKY, U.S. Pat. No. 1,658,833), which carry and position film cassettes of various selected sizes bearing x-ray sensitive film. In addition to the "bucky" tray other examples of tray systems known and used for this purpose are shown and described in U.S. Pat. Nos. 3,581,094 and 3,777,162.
The conventional x-ray film traya are believed to introduce potential inaccuracies in positioning the film because of the various adjustable bracing and clamping arrangements which are used. Inaccuracies may be introduced by improperly functioning clamping devices, or by careless or poorly trained technicians who take improper precautions when clamping or bracing the film. Such malfunctions or improper use will result not only in poor quality films and poor diagnosis, but also in subjection of the patient to undesirable and unnecessary radiation.
To overcome these problems, some x-ray machines have a collimator designed to operate automatically in response to electrical signals corresponding to the size and position of the cassette on the tray. However, even with such a device improper positioning or holding of the film cassette will cause improper signals to be transmitted to the collimator, resulting in the production of an x-ray beam of improper size or position. This could also unnecessarily produce radiation which is harmful to a patient.
The invention is directed to a tray for film cassettes which is believed to improve over these conventional trays.